In complex products, such as gas turbine engines, it is common to test components extensively prior to manufacture.
For many components a major form of testing is high cycle fatigue (“HCF”) testing. This generally relates to situations where more than 104 cycles are required before failure, the stress is low and the deformation experienced is primarily elastic.
Until now, HCF fatigue testing has typically been carried out either on a whole component, or a part of that component, the part being obtained by either extracting a sub-component or by machining away part of the original component. That component or sub-component would then be tested by exciting it at its resonant frequency or by forcing it into a ‘flutter’ type mode, until the component started to fail.
However, components are difficult to excite in complex vibration mode shapes, which often occur at higher frequencies, because of the increased energy required to drive them to exhibit such vibration modes. In particular the drive system used in the testing, which may be a chopped air jet, a piezo-electric exciter, an electro-mechanical shaker, a constant air-jet which causes an aero-elastic instability such as flutter, typically is not able to supply the necessary energy to drive the component at high frequencies.